America First was the name of an anti-semitic organization that opposed the entry of the U.S. on the side of England against Nazi Germany. CNN provides the background in a report after he used the phrase in a campaign speech. Fro that article:

After Pearl Harbor, the America First Committee closed its doors, but not before [Charles] Lindbergh made his infamous speech at an America First rally in Des Moines, Iowa, in September 1941. After charging that President Roosevelt had manufactured "incidents" to propel the country into war, Lindbergh proceeded to blurt out his true thoughts.

"The British and the Jewish races," he declared, "for reasons which are not American, wish to involve us in the war." The nation's enemy was an internal one, a Jewish one. "Their greatest danger to this country lies in their large ownership and influence in our motion pictures, our press, our radio, and our government," he contended. Booing began to drown out the cheers, forcing him again and again to stop, wait out the catcalls, and start his sentences over.

The organization is not Trump. But the echoes are well enough known that somebody with sound judgment might have avoided sounding them.

A report that climate change information had been deleted from the White House website has been disputed, at least insofar as whether past Obama material has been preserved.